1. The Field of the Invention
This invention relates to rotary compressors for compressing refrigerant in refrigeration systems, and, more particularly to a method and apparatus for removing contaminated oil from such a compressor and replacing it with fresh oil.
2. Description of the Prior Art
In general, a rotary compressor is of a construction wherein a rotary compressing device and an electric motor for driving the compressing device are completely enclosed within a sealed case. The motor typically occupies the upper part of the case and the compressing device is located in the lower part. The lower part of the case forms a sump for lubricating oil used in lubricating the moving parts of the compressing device. A gaseous refrigerant to be compressed is supplied from the outside, compressed by the compressing device, sent upwards through the rotor and the motor air gaps and delivered from the case through a discharge port at the upper end.
One application for such compressors are systems designed for recovering and purifying contaminated refrigerant from a refrigeration system prior to service being performed on the system. In a typical system of this type the compressor is used to withdraw the contaminated refrigerant from the unit being serviced. Usually filters and other purification devices are used to remove contaminants and oil from the refrigerant being withdrawn prior to it passing to the recovery compressor. Regardless of the efficiency of the purification system, however, contaminants will reach the recovery compressor and, with time, contaminate the lubricating oil of the recovery compressor.
It is accordingly desirable to be able to remove the contaminated oil from the recovery compressor and to recharge the compressor with a fresh quantity of lubricating oil. One arrangement for accomplishing this has been to provide a threaded drain plug in the compressor oil sump. This can be messy, and quite often, because such systems are usually contained within a confined cabinet, access to an oil drain fitting may be difficult. Once the oil is drained, replacing the oil with fresh oil, typically requires use of a pump to pump a new oil charge into the compressor through the open drain fitting.